Massachusetts Senate Candidates Pull Out All Stops Ahead of Election

As Massachusetts voters prepare to vote Tuesday in a special election to fill the Senate seat occupied by the late Sen. Ted Kennedy for 46 years, the candidates in the high-profile fight are pulling out all the stops.

State Attorney General Martha Coakley, the Democrat, unveiled a new TV ad today featuring President Obama stumping for her in Boston Sunday.

"Every vote matters, every voice matters. We need you on Tuesday," Obama is shown saying at the rally, where, in a scramble to keep the seat, he held a last-minute pep rally for Coakley, 56, and attempted to excite the Democratic base that dominates the state.

VIDEO: Massachusetts Senate Candidates Pull Out All Stops Ahead of ElectionPlay

The fight for Kennedy's old Senate seat has gone down to the wire between Coakley and Republican state Sen. Scott Brown, 50.

A longtime Democratic stronghold, Massachusetts is the last place Democrats would expect to become a battleground state. Both campaigns have spent millions of dollars in commercials, and volunteers have made hundreds of thousands of phone calls, and have come from as far away as Walla Walla, Wash. But the race is bigger than just Massachusetts. At stake is the president's health care reform initiative.

VIDEO: Massachusetts Senate Candidates Pull Out All Stops Ahead of ElectionPlay

If the special election Tuesday goes to Brown, Senate Democrats will lose the filibuster-proof 60-seat majority they currently enjoy. They need 60 votes to pass a health care bill and other Democratic priorities over Republican objections.

Brown, a lawyer and former model, has vowed to vote against health care overhaul if he is elected.

"As the 41st senator I can at least allow them to, you know, maybe look at things a little differently," Brown told ABC News in an interview.

ABC News video of Martha Coakley campaigning the day before the election.Play

Today Coakley invoked the memory of civil rights leader Martin Luther King Jr. to make her pitch.

"If Dr. King were here today, he'd be standing with us," she said. "And I know that he would be standing with us on the front line for health care, not as a privilege but as a right."

A GOP Win Could Thwart Health Care Reform

If Massachusetts Coakley loses, as polls indicate she might, Democrats want to be in a position to get a health-care bill through the Senate before Brown is sworn in, which wouldn't leave Democrats much time to hash out a compromise between the House and Senate bills.

VIDEO: The future of health care hinges on the race for Ted Kennedys seat. Play

Sources say that in case of a Democratic loss, the White House would want the House to vote directly on the bill the Senate passed on Christmas Eve. House Speaker Nancy Pelosi, D-Calif., has told White House officials they don't have enough votes to pass that version, but administration officials argue that if it's not the Senate bill, there may not be any health care overhaul.

If Brown wins and turns the seat Republican, another idea Democrats are discussing would have Senate Democrats force the bill through by bypassing normal Senate rules and passing the legislation through reconciliation, which requires only 50 votes. That would allow some moderates to peel away.

"There's no question that the president's domestic agenda hangs in the balance," said Democratic commentator Donna Brazile.

Video of ABC News Top LinePlay

Brown is running a campaign appealing to voter anxiety over the economy.

In the latest ABC News/Washington Post poll, 62 percent of Americans think the country is on the wrong track.

"Call it anger, call it frustration, call it sadness, call it whatever you want," Brown told ABC News.

Brown says he is an independent Republican, but could not say how he would vote differently than Republicans in Washington.

On Sunday in Boston to promote Coakley's candidacy, Obama tied Brown's agenda to "Washington Republicans" who are against financial reform, clean energy and health care reform.

"When the chips are down, when the tough votes come, on all the fights that matter to middle class folks of the Commonwealth, who is going to be on your side?" the president asked the crowd at Northeastern University in Boston.

VIDEO: The president fights to keep Sen. Kennedys Senate seat for the Democrats.Play

Massachusetts Senate Race Heats Up

Meanwhile, Brown disregarded the president's rhetoric yet seized on that same message of change that Obama successfully ran on in his own presidential campaign.

"They are tired of business as usual," Brown said. "They want someone who isn't part of the machine or an insider."

Joseph L. Kennedy, a Libertarian who is running as an independent, is also on the ballot but he hasn't been in the forefront. He has no relation to the Kennedy family.

While the president tried to rally the crowd on Sunday, he also attempted to distance himself from the election. Obama also acknowledged voter anger and frustration, which Brown has tapped into in his campaign.

"Where we don't want to go is backwards towards the same policies that got us into this mess in the first place. We have had one year to make up for eight. It hasn't been quick, it hasn't been easy, but we're beginning to deliver on the change you voted for," the president said. "A lot of these measures are going to rest on one vote in the U.S. Senate."

Obama steered clear of the topic of health care overhaul, which has become the focal point of this high-profile race.

The president instead took a swipe at Brown's description of himself as someone who drives a truck.

"I'd think long and hard about getting in that truck with Martha's opponent," the president said. "It might not take you where you want to go."

"If you were fired up in the last election, I need you more fired up in this election! I need you, I need you!" Obama told the crowd, estimated to be around 1,100.

Coakley today addressed the issue of economy that Brown has made the defining feature of his populist campaign.

"I wish there were easy answers to the tough problems we have," she said at a breakfast today commemorating Martin Luther King Jr. "Do not forget that they are problems that were not created by, but inherited by, our president, Barack Obama."

Candidates on both sides of the tight race have seen money and resources pouring in for their campaigns. Brown raised more than a million dollars online every day last week, according to a Republican source familiar with his fundraising. Bush administration official Karl Rove told his twitter followers to phone bank. Sen. John McCain called on to his supporters to back Brown.

Closeness of the Race Spells Trouble for Democrats

On the other side, Democratic groups placed more than 500,000 calls on Saturday. Former president Bill Clinton appeared with Coakley at two campaign events, and Kennedy's widow, Vicki, appeared in a television ad to support the attorney general. Last week, Obama taped a robo-call in support of Coakley.

"In Washington, I'm fighting to curb the abuses of a health insurance industry that routinely denies care. I'm fighting for financial reforms to stop Wall Street from playing havoc with our economy. I'm fighting to create a new clean energy economy," the president said in the call.

"And it's clear now that the outcome of these and other fights will probably rest on one vote in the United States Senate," he said.

National Democrats are shocked that the race seems this close, given that Democrats outnumber Republicans in Massachusetts 3-1. Some say it is less about the president and more about a weak candidate. Although Coakley made her name as a hard-nosed prosecutor in the famed Louise Woodward nanny trial in the 1990s, some Democrats say she has run a flat , flawed campaign. For example, last week she called former Red Sox baseball player and hometown hero Curt Schilling a Yankees fan, for supporting Brown.

But some Republicans say the mere closeness of the race spells troubles for Democrats.

"Whether Coakley wins or loses, the message is the same, health care. This health care package is death for candidates," said conservative commentator Tucker Carlson.

ABC News' Jake Tapper, Jonathan Karl and Kristina Wong contributed to this report.